Quantum information
hideIn quantum mechanics, quantum information is physical information that is held in the "state" of a quantum system. The most popular unit of quantum information is the qubit, a two-level quantum system. However, unlike classical digital states (which are discrete), a two-state quantum system can actually be in a superposition of the two states at any given time.
Quantum information differs from classical information in several respects, among which we note the following:
However, despite this, the amount of information that can be retrieved in a single qubit is equal to one bit. It is in the processing of information (quantum computation) that a difference occurs.
The ability to manipulate quantum information enables us to perform tasks that would be unachievable in a classical context, such as unconditionally secure transmission of information. Quantum information processing is the most general field that is concerned with quantum information. There are certain tasks which classical computers cannot perform "efficiently" (that is, in polynomial time) according to any known algorithm. However, a quantum computer can compute the answer to some of these problems in polynomial time; one well-known example of this is Shor's factoring algorithm. Other algorithms can speed up a task less dramatically - for example, Grover's search algorithm which gives a quadratic speed-up over the best possible classical algorithm.
Quantum information, and changes in quantum information, can be quantitatively measured by using an analogue of Shannon entropy. Given a statistical ensemble of quantum mechanical systems with the density matrix S, it is given by
Many of the same entropy measures in classical information theory can also be generalized to the quantum case, such as the conditional quantum entropy.
For more information about Quantum information, read the full article at
Wikipedia.
This text uses material from Wikipedia and is available under the GNU Free Documentation License.
News tagged with quantum information
Physicists Demonstrate Three-Color Entanglement
Oct 07, 2009 |
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(PhysOrg.com) -- For the first time, physicists have demonstrated the quantum entanglement of three light beams, all of different wavelengths. Entanglement of two light beams of different wavelengths has already ...
Building a better qubit: Combining 6 photons together results in highly robust qubits
Oct 05, 2009 |
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Exploiting quantum mechanics for transmitting information is a tantalizing possibility because it promises secure, high speed communications. Unfortunately, the fragility of methods for storing and sending ...
Physicists work to understand atomic collisions important to ultracold quantum gasses
Sep 30, 2009 |
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A Kansas State University physicist is continuing his study of atomic collisions with the help of a National Science Foundation grant awarded under the American Recovery and Reinvestment Act.
Physicists Investigate Unusual Four-Qubit Entanglement
Sep 30, 2009 |
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(PhysOrg.com) -- For the first time, physicists have experimentally demonstrated a four-qubit bound-entangled state - a peculiar form of entanglement that cannot be distilled (optimized) by the usual means. ...
Diamonds May Be the Ultimate MRI Probe, Say Quantum Physicists
Sep 22, 2009 |
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(PhysOrg.com) -- Diamonds, it has long been said, are a girl's best friend. But a research team including a physicist from the National Institute of Standards and Technology has recently found that the gems ...
First-ever calculation performed on optical quantum computer chip
Sep 03, 2009 |
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(PhysOrg.com) -- A primitive quantum computer that uses single particles of light (photons) whizzing through a silicon chip has performed its first mathematical calculation. This is the first time a calculation ...
Pushing quantum mechanics to higher levels
Aug 11, 2009 |
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Scientists at UC Santa Barbara have devised a new type of superconducting circuit that behaves quantum mechanically -- but has up to five levels of energy instead of the usual two. The findings are published ...
Sustained quantum information processing demonstrated
Aug 06, 2009 |
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Raising prospects for building a practical quantum computer, physicists at the National Institute of Standards and Technology have demonstrated sustained, reliable information processing operations on electrically ...
Quantum measurements: Common sense is not enough
Jul 22, 2009 |
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(PhysOrg.com) -- In comparison to classical physics, quantum physics predicts that the properties of a quantum mechanical system depend on the measurement context, i.e. whether or not other system measurements ...
Quantum memory and turbulence in ultra-cold atoms
Jul 20, 2009 |
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Scientists at MIT have figured out a key step toward the design of quantum information networks. The results are reported in the July 20th issue of Physical Review Letters and highlighted in APS's on-line journa ...
Physicists Propose Scheme for Teleporting Light Beams
Jul 14, 2009 |
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(PhysOrg.com) -- Usually when physicists talk about quantum teleportation, they're referring to the transfer of quantum states from one particle to another without a physical link. Now, physicists have investigated ...
Tying up loose ends for a quantum leap
Jul 10, 2009 |
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Quantum technologies have become the Holy Grail of the IT industry with research projects springing up all over Europe. Now a major effort is being made to spur development by adopting a coordinated, structured approach.
Scientists create first electronic quantum processor
Jun 28, 2009 |
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A team led by Yale University researchers has created the first rudimentary solid-state quantum processor, taking another step toward the ultimate dream of building a quantum computer.
Scientists demonstrate all-fiber quantum logic
May 28, 2009 |
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A team of physicists and engineers have demonstrated all-fibre quantum logic, where single photons are generated and used to perform the controlled-NOT quantum logic gate in optical fibres with high fidelity.
Too much entanglement can render quantum computers useless
May 25, 2009 |
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(PhysOrg.com) -- "For certain tasks, quantum computers are more powerful than their classical counterparts. The task to be performed is the same for quantum or classical systems. However, the former ones can do it in a more ...
